Lens polishing overlay



July 3, 1956 w. c. SEIFERT LENS POLISHING ovERLAY Filed Sept. 4, 1953 GWR T R H m n L P m.. n

IN VENTOR W/LL/AM C SEI/:ERT

ATTORNEY United States Patent LENS PGLISHIN G OVERLAY William C.Seifert, Narbeth, Pa., assignor to Donald W. Kent, Philadelphia, Pa.

Application September 4, 1953, Serial No. 378,527

l Claim. (Cl. 51-195) This invention is a new and useful overlay for andmethod of grinding glass blanks, for example lens blanks, for theproduction of optical lenses. The invention will be fully understoodfrom the following description read in conjunction with the drawings inwhich:

Fig. l is an exploded perspective view of an overlay to be used inapplying the invention;

Fig. 2 is a top view on an enlarged scale of the top layer shown in Fig.l;

Fig. 3 is a section taken on line 3-3 of Fig. 2;

Fig. 4 is a vertical section through the apparatus in which the grindingand/ or polishing may be carried out; and

Fig. 5 is a plan view of one element of the showing in Fig. 4.

Referring to Fig. l, the elements in composite tape 1 which constitutesthe overlay are as follows:

Separating layer 2 is a ribbon of non-adhesive or only slightly adhesivematerial designed to permit the overlay 1 to be assembled in layers orwound upon itself, but still readily separable as parts of it arerequired for use. Separating layer 2 may be paper impregnated with ahigh M. P. wax or may be a thin sheet of poly-per-fluor-ethylene or anyother suitable material which is easily separable, i. e. eithernon-adhesive or only slightly adhesive. Layer 3 is a ribbon (forexample, thin cloth) coated on both sides with a suitable adhesive toenable it to adhere firmly to any metal surface against which it may bepressed. Such adhesives are known in the art and, therefore, need not bemore fully discussed. Layer 4 is of optical pitch such as wood resin,bees wax or some other thermoplastic material preferably with asoftening point below 100 C. Materials with suitable characteristics arerecognized in the art under the general designation of optical pitch.This layer is preferably formed by pouring the material in moltencondition onto the ribbon 3 while in level position and then permittingthe pitch to cool and freeze in layer form. The margins of the pitch canbe fixed by mold boards. Alternatively, the overlay may be initiallyformed in sheets and slit in ribbon (tape) form after completion. Thelayer of optical pitch preferably is several times the thickness ofadhesive layer 3 and may conveniently be from JAG to A6 of an inch.Layer 5 is a ribbon preferably of thin sheet fibrous felted materialwith a crinkled surface. The surface ridges are preferably of the orderof about 1/32 of an inch apart and a few thousandths of an inch abovethe valleys. A sulfite pulp paper doctored to develop a crinkled surfacesuch as paper towel stock has been found satisfactory. This material isimpregnated with a water insoluble plastic material such as apolymerized unsaturated high molecular weight hydrocarbon. Examples ofsuch hydrocarbons are polythene, poly-per-uor-ethylene, polybutylene andpolyvinyl chloride. The impregnating material must not fill the valleysand destroy the aforementioned relief characteristics. Although theseimpregnants are normally non-adhesive, they are laid down on layer 4while the optical pitch is still in molten condition and so develop astrong adhesion to the optical pitch.

An overlay of the material described is preeminently 2,752,737 PatentedJuly 3, 1956 suited to polishing. If grinding is desired, element 5 maybe of metal foil and preferably a metal foil consisting predominantly ofnickel as more specifically disclosed in my co-pending applicationSerial No. 378,526.

Overlay 1 is assembled for convenience into bundles of flat strips or,alternatively, may be wound in rolls while the pitch is thermoplastic.

The method of use will be evident from the showing in Figs. 4 and 5.Referring to Fig. 5, separating layer 2 is first removed and theremainder, consisting of layers 3, 4 and 5, is heated lightly, forexample by sweeping over it several times a small flame such as thatprovided by a Bunsen burner. This heating is continued to a point atwhich the pitch is just thermoplastic. At this point, a series of strips6 of the overlay are (Fig. 5) applied to spherical or aspherical surface7 of the supporting form 8 defining the desired surface to which theblank is to be finished and pressed against this surface to causeadhesive layer 3 to attach itself firmly to this surface. The ends arethen trimmed roughly to the margin of surface 7, as indicated in Fig. 5.The lens blank is secured to holder 10 by pitch 11 or in any othersuitable way. The glass blank or a master curve is pressed againststrips 6 while the pitch is still thermoplastic thereby causing theexposed surface of the strips to conform to the surface of the glassblank or master curve.

As soon as the optical pitch in strips 6 has hardened, the overlay isready for use. If the glass blank is to be ground, the strips faced withmetal foil are used and a slurry of an abrasive material is fedcontinuously or intermittently to the grinding surface while the lensblank 9 is worked against the surface of the strips. The strips willsurvive a large number of grindings and after they have become worn orshould be removed for any other reason, they are easily detachedmanually.

If the glass blank 9 is to be polished, the strips 6 will be thoseprovided with a face of impregnated, fibrous material defining acrinkled surface as hereinabove described. In this case, an aqueoussuspension of rouge will be fed either continuously or intermittently tothe polishing surface while the previously ground glass blank is beingworked against the polishing surface.

This method of polishing has been tested against the various acceptedmethods of polishing to finish optical lenses and found to produce aperfect finish in approximately one fourth of the time required by themethods now in use and with a higher degree of uniformity.

Surfaces such as those formed by ribbon 5, whether of metal foil toretain abrasive, or of impregnated fibrous material to cause the rougeto exert its polishing effect, Will be generically designated ascharging surfaces.

I claim:

An overlay for glass polishing in the form of a composite tape includinga .ribbon of adhesive material, a ribbon of thermoplastic optical pitchof at least 1/16 in thickness adhering to said ribbon of adhesivematerial, a ribbon of rouge retaining material carried by and adher ingto said ribbon of optical pitch, said rouge retaining materialconsisting of paper defining a crinkled surface and impregnated With awater insoluble plastic material while retaining the elevations anddepressions of said crinkled surface.

References Cited in the file of this patent UNITED STATES PATENTS369,431 Brown Sept. 6, 1887 1,560,033 Bart Nov. 3, 1925 2,024,303 ObrigDec. 17, 1935 2,059,583 Jackson et al Nov. 3, 1936 2,485,295 Larson Oct.18, 1949 2,544,940 Ritterbusch et al. Mar. 13, 1951

